robotics for u_ ir sensors from scratch + line follower

8/4/2019 ROBOTICS for U_ IR Sensors From Scratch + Line Follower

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NEWTONS LAW's Re'coded

WEDNESDAY, JUNE 18, 2008

IR sensors From Scratch + Line follower

IR emitter and IR phototransistor

An infrared emitter is an LED made from gallium arsenide, which emits near-infrared

energy at about 880nm.

The infrare d phototransistor acts as a transistor with the base voltage determ ined by the

amount of light hitting the transistor.

Hence it acts as a variable current source. Greater amount of IR light cause greater

currents to flow through the collector-emitter leads.

As shown in the diagram be low, the phototransistor is wired in a similar configuration to

the voltage divider.

The variable current traveling through the resistor causes a voltage drop in the pull-up

resistor.

This voltage is measured as the output of the device

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Schematic Diagram for a Single Pair of Infrared Transmitter and Receiver

To get a good voltage swing , the va lue of R1 must be carefully chosen. If Rsensor = a

when no light falls on it and Rsensor = b when light falls on it. The difference in the two

potentials is:




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If the emitter and detector (aka phototransistor) are not blocked, then the output on pin 2

of the 74LS14 will be high (apx. 5 Volts).

When they are blocked, then the output will be low (apx. 0 Volts). The 74LS14 is a Schmitt

triggered hex inverter.

A Schmitt trigger is a signal conditioner. It ensures that above a threshold value, we will

always get "clea n" HIGH and LOW signals.

Not Blocked Case: Pin 2 High Current from Vcc flows through the detector. The current

continues to flow through the base of Q2.

Current from Vcc also flows through R2, and Q2's Drain and Emitter to ground.

As a result of this current path, there will be no current flowi ng through Q1's base.

The signal at U1's pin 1 will be low, and so pin 2 will be high. Blocked Case: Pin 2 Low

Current "stops" at the detector.

Q2's base is not turned on. The current is re-routed pa ssing through R2 and into the base

of Q1.

This allows current to flow from Q1's detector and e xiting out Q1's emitter. Pin 1 i s thus

high and pin 2 will be low.

To detect a line to be followed, we are using two or more number of poto-reflectors.

Its output current that proportional to reflection ra te of the floor is converted to volta ge

with a resister and tested it if the line is detected or not.

However the threshold voltage cannot be fixed to any level because optical current by

ambent light is added to the output current.

Most photo-detecting modules are using modurated light to avoid interference by the

ambient light.

The detected signal is filtered with a band pass filter and disused signals are filtered out.

Therefore only the modurated signal from the light emitter can be detected.

Of course the detector must not be saturated by a mbient light, this is effective w hen the

detector is working in linear region.




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Posted by Faizy at 11:02 PM

Labels: line follower, SENSORS

The line position is compeared to the center value to be tracked, the position error is

processed with Proportional/Integral/Diffence filters

to generate steering command. The line folloing robot tracks the line in PID control thatthe most popular argolithm for servo control.

The proportional te rm is the commom process in the servo system. It is only a gain

amplifire without time dependent process.

The differencial term is applied in order to improve the responce to disturbance, and it

also compensate phase lag at the controled object.

The D term will be required in most case to stabilize tracking motion. The I term that

boosts DC gain is applied in order to remove left offset error,

however, it often decrease servo stability due to its phase lag.

When any line sensing error has occured for a time due to getting out of line or end of

line, the motors are stopped and

the microcontroller enters sleep state of zero power consumption.

Typical Examples of infrared Transmitter and Receiver installation

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February 23, 2010 11:59 AM

Faizy said...

@ Navrati

When you have intersections, try to count the number of intersections, so that when you start

next time you can travel with much ease.

An other thing, if you have to take a turn at intesection, the position of wheels should be in

line with the intersection line. Hope you got it.

February 28, 2010 1:18 PM

akinaktugaksoy said...

i am trying to build a heatbeat finger sensor.which ir-led and phototransistors should i

choose.they must be at same frequency working length.and the value of R1 is 39K.so which

photo transistor must placed there? i have a shematic for this project but i couldnt find

models of photo transistor and ir-led.

January 1, 2011 2:53 PM

BALASUBRAMANIANsaid...

could anyone tell me how i can m ake my line follower bot detect lines n m ake turns at high

speed about 300rpm?????

March 6, 2011 3:54 AM

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